Silicon-bridged transition metal compounds

ABSTRACT

Silicon-bridged transition metal compounds and their use as α-olefin polymerization catalysts are disclosed. A chiral silicon-bridged metallocene catalyst polymerizes α-olefins to high isotacity with a minimum of inversions at high rates of catalyst activity. The catalyst is easily made in high yields and readily separated from atactic meso forms.

This application is a continuation of U.S. Ser. No. 07/661,274, filedFeb. 26, 1991, now issued as U.S. Pat. No. 5,120,867; which is adivisional of U.S. Ser. No. 07/405,090 filed Sep. 7, 1989 now issued asU.S. Pat. No. 5,017,714, which is a continuation of U.S. Ser. No.07/170,516 filed Mar. 21, 1988, now abandoned.

FIELD OF THE INVENTION

The invention pertains to silicon-bridged metallocene compounds havingutility as catalysts for stereoregular α-olefin polymerization.

BACKGROUND OF THE INVENTION

There are four types of tacticity which have been described inpoly-α-olefins: atactic, normal isotactic, isotactic stereoblock, andsyndiotactic. Although all of these tacticity variations have beenprimarily demonstrated in the case of polypropylene, they are in theoryequally possible for all poly-α-olefins. The random, or atacticstructure is represented by a polymer backbone of alternating methyleneand methine carbons, with randomly oriented branches substituting themethine carbons. The methine carbons randomly have R and Sconfigurations, creating adjacent pairs either of like configuration (ameso or "m" dyad) or of unlike configuration (a racemic or "r" dyad).The atactic form of a polymer will contain approximately equal fractionsof meso and racemic dyads.

In the normal isotactic structure of an α-olefin polymer, all of themonomer units have the same stereochemical configuration, with theexception of random errors which appear in the chain. Random errors willalmost always appear as isolated inversions of configuration which arecorrected in the very next insertion to restore the original R or Sconfiguration of the propagating chain. These single insertions ofinverted configuration give rise to rr triads, which distinguish thisisotactic structure in its NMR from the isotactic stereoblock form. Longbefore anyone had discovered a catalytic system which produced theisotactic stereoblock form of a poly-α-olefin, the possible existence ofsuch a structure had been recognized and mechanisms for its formationhad been proposed based on conventional Ziegler-Natta mechanisms inLanger, A. W., Lect. Bienn. Polym. Symp. 7th (1974); Ann. N. Y. Acad.Sci. 295, 110-126 (1977). The first example of this form ofpolypropylene and a catalyst which produces it in a pure form werereported in Ewen, J. A., J. Amer. Chem. Soc., v. 106, p. 6355 (1984).

The formation of stereoblock isotactic polymer differs from theformation of the normal isotactic structure in the way that thepropagation site reacts to a stereochemical error in the chain. Asmentioned above, the normal isotactic chain will return to the originalconfiguration following an error because the stereochemical regulator,the metal and its surrounding ligands, still dictates the samestereochemical preference during insertion. In stereoblock propagation,the site itself changes from one which dictates an R configuration toone which dictates an S configuration. This occurs either because themetal and its ligands change to the opposite stereochemicalconfiguration or because the configuration of the last added monomer,rather than the metal chirality, controls the configuration of the nextadded monomer. The former case, where the metal changes to the oppositeconfiguration, has been sought but, as far as applicant is aware, hasnever been observed in a Ziegler polymerization; however, the lattercase is now known to be responsible for stereoblock polymerization.

Unlike normal isotactic polymers, the lengths of individual blocks ofthe same configuration in the stereoblock structure vary widely due tochanging reaction conditions. Since only the erroneous parts of thechains affect the crystallinity of the product, in general, normalisotactic polymers and isotactic stereoblock polymers of long blocklength (greater than 50 isotactic placements) have similar properties.

Syndiotactic polymers have a strong mechanistic similarity to isotacticstereoblock polymers; indeed, the force which results in syndiotacticpropagation is the same steric interaction of the last added monomerwith the incoming monomer. The most significant difference between theisotactic propagation mechanisms and the syndiotactic propagationmechanism is the mode of addition, which defines which carbon atom ofthe new monomer becomes bonded to the metal during the insertion step,as reported in Boor, Jr. J., Ziegler-Natta Catalysts andPolymerizations, Academic Press, New York 1979. The addition modes ofisotactic and syndiotactic propagation are opposite.

Syndiotactic propagation has been studied for over 25 years; however,only a few good syndiospecific catalysts have been discovered, all ofwhich are extremely sensitive to monomer bulkiness. As a result,well-characterized syndiotactic polymers are limited only topolypropylenes. The chain backbone of a syndiotactic polymer can beconsidered to be a copolymer of olefins with alternating stereochemicalconfigurations. Highly syndiotactic polymers are generally highlycrystalline and will frequently have higher melting points than theirisotactic polymorphs. However, the frequency of errors in typicalsyndiotactic polymers (mr triads) is much greater than in the relatedisotactic stereoblock polymers, possibly due to weaker monomerorientation forces in these catalysts. A frequent error in syndiotacticpolypropylenes is an isotactic block of monomers. Mechanisms for theformation of several hypothetical types of stereoregularity, consistingof non-random blocks of the above stereoregular structures, have beenproposed in Boor and Langer mentioned above.

Chirality, whether it arises from catalyst crystal structure,surrounding ligand structure, or asymmetry of the growing chain, isessential to polymerize stereoregularly. Polymerization catalysts whichlack chirality or have weak or distant asymmetry in their structureswill produce either atactic polyolefins or ones of low stereoregularity.The mechanisms by which metallocene catalysts control chain tacticityare based on the same principles as for both conventional andmetal-halide catalysts. The identification of two distinct types ofcatalyst chirality has given rise to two mechanisms for stereochemicalinduction during polymerization termed the `site control mechanism` andthe `chain end control mechanism`. For many years there were ongoingarguments about what mechanistic step and what features of thepolymerization process played the most important role in stereospecificpolymerization. Today, while the arguments have quieted, there is stillno single mechanistic interaction which fully explains stereoregularpropagation for all of the known stereospecific catalysts, including themetallocenes. Some of the key proposals are reviewed by Boor mentionedabove and include: (1) the crystalline asymmetry of the active site, (2)the asymmetry induced by cocatalyst binding, (3) asymmetry introduced bythe attached polymer helix, and (4) the asymmetry of the assembledactive site. Rather than to select any one effect as most important, thetwo present-day mechanisms of stereoregulation divide these steric andchiral effects either into catalyst site or chain-end interactions. Eventhough catalyst site chirality will almost always dominate overchain-end chirality, the chain-end control mechanism in achiral catalystis responsible for two of the most interesting types of tacticity,steroblock isotacticity and syndiotacticity.

One of the key features of the chain-end control mechanism forcoordinated olefin polymerization is the mode of olefin addition duringthe propagation step. The two types of olefin addition, primary additionand secondary addition, are shown in the following diagram forpolypropylene: ##STR1## These addition mechanisms are also referred toas `1-2 addition` and `2-1 addition`, respectively, indicating thecarbon number of the last monomer and the carbon number of the newmonomer which will form the new bond. Primary addition is almostexclusively the mode of addition found for titanium and zirconiumcatalysts, including metallocene and non-metallocene types and mostheterogeneous vanadium catalysts. Secondary addition is common forcatalysts in which the alkyl is more `cationic`, such as solublevanadium catalysts used in low temperature polymerizations. In all caseswhere the mode of addition has been studied in Ziegler-Natta catalysis,primary insertion has accompanied isotactic polymerization and secondaryinsertion has accompanied syndiotactic polymerization, although theconverse is certainly not true. When visualizing the insertion stepusing (I) and (II), it is important to remember that olefin insertion inZiegler-Natta polymerization always takes place in a CIS manner, asshown, meaning that the coordinated face of the olefin always attachesto the existing alkyl-metal bond. Inversion of neither the alkyl carbonconfiguration nor the olefin-metal carbon configurations occurs, asoriginally reported by Natta, G., et al, Chem. Ind. (Milan) 42, 255(1960), and later confirmed by Zambelli et al, Makromol. Chem. 112, 183(1968).

A close examination of the above figures (I) and (II) for points ofsteric interactions between the olefin side chain and the attachedpolymer chain leads to a conclusion that the overall steric influencesare much greater for primary addition than for secondary addition. Thissteric difference manifests itself in several ways: (1) a lower relativereactivity of substituted olefins in the primary addition mode (highercopolymerization r values for titanium versus vanadium), and (2) ahigher temperature at which chain-end controlled isotacticity (-10° C.)can be achieved relative to chain-end controlled syndiotacticity (-60°C.).

If the metal and its ligands (L) are achiral in these figures, the onlychirality which develops during the insertion step is due to the chiralcarbons along the polymer chain itself. In isotactic stereoblock andsyndiotactic polymerization it is this rather weak chirality thatdirects the new monomer to one of two possible orientations relative tothe polymer chain's last added monomer during insertion. Regardless ofthe fact that the growing chain can rotate freely and shift among thevacant coordination sites of the metal, the last added monomer, in eachcase, will exert an orienting effect on an olefin seeking coordination.If this orientation energy is large compared to the randomizing effectsof kT, it can be shown with models that a tactic polymer will result. Itcan be shown, in fact, that an isotactic polymer will result fromprimary addition.

Although every second carbon of the polymer backbone of a growingpoly-α-olefin chain is chiral, it has been shown in many differentexperiments that the effect of this chain chirality is not sensed beyondthree bonds separation from the metal as reported in Zambelli et al,Macromolecules, v. 16, pp. 341-8 (1983). In addition, adequate chiralityfor tactic propagation may not be sensed when the differences betweenthe groups forming the chiral center become smaller. Such effects can bequite profound. Propylene, which introduces a chiral carbon centerbonded to a hydrogen, a methyl group, and a polymer chain, is the onlyα-olefin which is readily polymerized by the chain-end control mechanismto an isotactic stereoblock and a syndiotactic polymer. For higherα-olefins, the larger steric bulk of the olefin branch and itssimilarity to the polymer chain causes polymerization rates and/orstereoregularity to be severely depressed.

Heretofore, the most effective way to produce isotactic poly-α-olefinsfrom metallocene-alumoxane catalysts has been to use a metallocene whichhas chirality centered at the transition metal as reported in Ewen, J.A., J. Amer. Chem. Soc., v. 106, p. 6355 (1984) and Kaminsky, W., et al,Agnew. Chem. Int. Ed. Eng.; 24, 507-8 (1985). The best knownconventional Ziegler-Natta catalyst which polymerizes olefins to normalisotactic structures, TiCl₃, also has metal centered chirality which thetitanium acquires by being located at specific edge and defect sites onthe crystal lattice. Both titanium and zirconium metallocenes containinga 1,2-ethylene bridged indenyl (or a tetra-hydroindenyl) ligand in theracemic form are good examples of such chiral metallocene catalystswhich produce poly-olefins of the normal isotactic structure. Theasymmetric steric environment of the metal in each of these catalystsinduces a reproducible orientation of the incoming monomers, which is amechanistic requirement in addition to CIS primary addition that must bemet by a catalyst in order to polymerize stereoregularly. When catalystsite chirality is unchanging and primary addition occurs, normalisotactic polymers result.

FIGS. 1-4 demonstrate for TiCl₃ and for two chiral forms and onenon-chiral form of metallocenes how metal centered chirality can directisotactic polymerization. In FIG. 1 a titanium trichloride center whichis complexed to a dialkyl aluminum chloride and a growing polymer chainis represented. The chirality contributed by the crystalline TiCl₃ sitealone has been reputed to be of foremost importance in this mechanism inNatta, J. Inorg. Nucl. Chem. 8, 589 (1958). While additional chiralitycontributed by coordinated aluminum alkyls, bound chiral polymer chains,and added third components has been reported to produce observableeffects in Boor, Langer and Zambelli et al (1983) mentioned above, theseact primarily to enhance the isotacticity by increasing the steric bulkaround the site. Generally such `modifiers` simultaneously decrease thepolymerization rate at a site as they increase its isotacticity.

In FIG. 1, a vacant monomer coordination site is indicated by the opensquare. Monomer coordination at this site occurs only with the olefinbranch pointing in one direction due to severe steric interactions inthe other configuration. If the polymer chain Pn were to shift to thevacant position, monomer coordination must occur in the oppositeconfiguration at the newly opened vacant site. Sites of both chiralconfigurations, created by a shift in the position of the polymer chain,as implied above, are though not to occur in crystalline TiCl₃ systemsas reported in langer, mentioned above. In these systems, the two sitesclearly do not have equivalent steric and electronic requirements.

Chiral metallocenes which polymerize alpha-olefins to normal isotacticpolymers have many structural similarities to the crystalline titaniumcatalysts. In these soluble metallocene-alumoxane catalysts, however,chirality is imposed on the metal center by the asymmetric metalloceneligand, rather than by a crystalline lattice of chloride ions. FIG. 2shows the R and S (mirror image) forms of the racemic 1,2-ethylenebridged bis-tetra-hydroindenyl zirconium (IV) catalyst reported in Wildet al, J. Organomet. Chem. 232, 233-47 (1982) and Ewen and Kaminsky,mentioned above. FIG. 3 indicates how the monomer, on binding, isoriented by the chiral projections of the ligand. Both of the racemicindenyl catalyst structures satisfy all the criteria for stereoregularpolymerization, including that shifting the polymer chain to theopposite coordination vacancy causes the catalyst to direct the monomerto bind in the opposite configuration. This criterion, thought not to beapplicable to titanium chloride catalysts, may have greater importancefor these metallocene catalysts since the two coordination sites wherethe polymer and monomer bind should be equivalent sterically andelectronically.

The structure shown in FIG. 4, a bridged tetra-hydroindenyl isomer, isachiral since it has a plane of symmetry which intersects the metal atombetween the planes of the metallocene rings. As expected, this mesoisomer does not orient the monomer at either coordination vacancy and,as a result, does not polymerize stereoregularly by the catalyst sitecontrol mechanism. The chain end control mechanism would still enablethis catalyst to form isotactic stereoblock polymer by the chain-endcontrol mechanism under conditions described in U.S. Pat. No. 4,522,482.

Topping the list of metallocene structures which have been shown topolymerize stereoregularly are the ethylene bridged bis-indenyl andbis-tetra-hydroindenyl titanium and zirconium (IV) catalysts discussedabove. These catalyst structures were synthesized and studied in Wild etal (1982) mentioned above, and were later reported in Ewen and Kaminskyet al, mentioned above, to polymerize α-olefins stereoregularly whencombined with alumoxanes. It was further disclosed in West German Off.DE 3443087A1 (1986) without giving experimental verification, that thebridge length can vary from a C₁ to C₄ hydrocarbon and the metallocenerings can be simple or bicyclic but must be asymmetric.

Another type of catalyst chirality is formed by arranging non-chiralligands in a chiral manner around the catalytic metal center. Manychiral complexes of this type can be mentally formulated in a shorttime; however, since none of these structures have induced isotacticityin poly-α-olefins as far as the applicant is aware, only a few reportedstructures will be mentioned here, including those structures thestereoregulating ability of which has been tested. The failure of thesestructures to polymerize stereoregularly must indicate that their sitechirality is either lost in the active state of the catalyst, such asmight happen in a three-coordinate cationic intermediate, or isinsufficient to orient the monomer. Martin et al, J. Organomet. Chem.97, 261-273 (1975) and Couturier et al, J. Organomet. Chem. 195, 291-306(1980), have reported the preparation of a large number of titanium andzirconium derivatives of this type as follows:

    ______________________________________                                        Metallocene      Tacticity                                                    ______________________________________                                        (CpMe.sub.5) Cp Zr Me Cl                                                                       No isotactic PP observed                                     (CpR) Cp Zr Et Cl                                                                              "                                                            (CpR) (CpR') Zr Me Cl                                                                          "                                                            (CpMe.sub.5) Cp Ti (C.sub.6 F.sub.5) Cl                                                        "                                                            (Indenyl) Cp Zr Me Cl                                                                          "                                                            ______________________________________                                    

Metallocenes which are chiral but do not contain a bridge can besynthesized by introducing a chiral group into one of the ligands. Inthese examples, one of the ligands rather than the metal is the `center`of the chirality. The resultant complexes have non-superimposible mirrorimages and thus are chiral and exist as R and S isomers. This type ofchirality will not be lost in a three-coordinate intermediate providedthat the chiral ligand is not lost. Martin et al and Couturier et almentioned above have also reported preparation of numerous compounds ofthis structure. The following compounds contain this type of chirality,but have not been shown to have the ability to polymerize propylenestereoregularly:

    ______________________________________                                        Metallocene*       Tacticity                                                  ______________________________________                                        rac-(methyl H.sub.4 -Indenyl).sub.2 Zr Cl.sub.2                                                  No isotactic PP observed                                   (R,S) Cp.sub.2 Zr (isobutyl) Cl                                                                  "                                                          (R'Cp) Cp Zr Cl.sub.2                                                                            "                                                          (R'Cp).sub.2 Zr Cl.sub.2                                                                         "                                                          ______________________________________                                         *R' = --CH.sub.2 CH(CH.sub.3)(C.sub.6 H.sub.5)                                    --CH(CH.sub.3)(C.sub.2 H.sub.5)                                               --CH(CH.sub.3)(C.sub.6 H.sub.5)                                      

It can thus be seen that there is a need for a catalyst whichpolymerizes α-olefins to high isotacticity with a minimum of inversions,is easily made in high yield and easily separated from meso formsthereof, and is capable of being tailored to meet the neededrequirements of polymerization activity and isotacticity.

SUMMARY OF THE INVENTION

The present invention provides a silicon-bridged metallocene catalyst.The racemic isomers of the catalyst polymerize α-olefins to highisotacticity with a minimum of inversions and can be tailored to highactivity and isotacticity. In addition, the catalyst is easily made inhigh yield and separated from meso forms.

In a broad aspect, the invention provides a chiral transition metalcompound which has the formula: ##STR2## in which M' is a transitionmetal, X' and X" are the same or different hydride, halogen, hydrocarbylor halohydrocarbyl having up to about 6 carbon atoms; A' and A" are thesame or different asymmetrical mononuclear or polynuclear hydrocarbyl orsilahydrocarbyl moieties; and S' is a silicon-containing bridge of 1-4atoms selected from silanylene, silaalkylene, oxasilanylene andoxasilaalkylene.

In another aspect, the invention provides a catalyst system including(i) a silicon-bridged chiral metallocene of the formula: ##STR3## inwhich M' is a transition metal, X' and X" are the same or differenthydride, halogen, hydrocarbyl or halohydrocarbyl having up to about 6carbon atoms; A' and A" are the same or different asymmetricalmononuclear or polynuclear hydrocarbyl or silahydrocarbyl moieties; andS' is a silicon-containing bridge of 1-4 atoms selected from silanylene,silaalkylene, oxasilanylene and oxasilaalkylene; and (ii) an alumoxaneselected from cyclic alumoxanes of the formula (R-Al-O)_(n) and linearalumoxanes of the formula R(R-Al-O)_(n) AlR₂, wherein each R isindependently C₁ -C₅ alkyl and n is an integer from 2 to about 25. Themetallocene-alumoxane catalyst can be usefully supported on a catalystsupport material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 (prior art) is a schematic representation of the polymerizationof propylene with titanium trihalide complexed with dialkyl aluminumhalide in which R represents alkyl and X represents halide;

FIG. 2 (prior art) is a representation of the R and S forms ofn-(1,1'-ethylene-bis(4,5,6,7-tetrahydroindenyl) zirconium;

FIG. 3 (prior art) is a schematic illustration of monomer orientationwith the zirconocene of FIG. 2;

FIG. 4 (prior art) illustrates monomer binding of the meso form ofn-(1,1'-ethylene-bis(4,5,6,7-tetrahydroindenyl) zirconium;

FIGS. 5-8 (prior art) illustrate the mobility of the chiral methylgroups of C₁ -C₄ bridged bis (methylcyclopentadienyl) zirconocenes withrespect to the metal atom;

FIG.9 is the H-1 NMR spectrum of racemic[1,1'-dimethylsilanylene-bis(4,5,6,7 tetrahydroindenyl)] zirconiumdichloride; and

FIG. 10 is a representation of the crystalline structure of[1,1'-dimethylsilanylene-bis(4,5,6,7 tetrahydroindenyl)] zirconiumdichloride.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The silicon-bridged metallocene compounds of the invention have thegeneral formula: ##STR4## in which M' is a transition metal, X' and X"are the same or different hydride, halogen, hydrocarbyl orhalohydrocarbyl having up to about 6 carbon atoms; A' and A" are thesame or different asymmetrical mononuclear or polynuclear hydrocarbyl orsilahydrocarbyl moieties; and S' is a silicon-containing bridge of 1-4atoms selected from silanylene, silaalkylene, oxasilanylene andoxasilaalkylene.

The transition metal M' in the above formula may be any transitionmetal, preferably a group IVB transition metal. Exemplary preferredtransition metals include titanium, hafnium and especially zirconium.

As mentioned above, the transition metal substitutents X' and X" may bethe same or different and are selected from hydride, alkyl, aryl,halogen, haloakyl, and haloaryl. X' and X" are preferably halogen or C₁-C₆ alkyl. Exemplary substituents include hydride, methyl, ethyl,propyl, butyl, pentyl, hexyl, cyclohexyl, phenyl, chloride, bromide,fluoride, iodide, and the like.

A' and A" may be any mononuclear or polynuclear hydrocarbyl orsilahydrocarbyl which is asymmetric. Preferably, A' and A" have theformula: ##STR5## wherein n is an integer from one to four and each R'is the same or different hydrocarbyl or silahydrocarbyl, preferably of1-20 carbon atoms and 0-2 silicon atoms, or taken together, two or moreof R' are hydrocarbylene or silahydrocarbylene, preferably of 1-20carbon atoms and 0-2 silicon atoms. As representative examples of R'there may be mentioned methyl, ethyl, butyl, propyl, hexyl, octyl,decyl, dodecyl, silyl, trimethyl silyl, propylene, butylene, butenylene,pentylene, pentenylene, hexylene, hexenylene, hexadienylene, phenyl,phenylene, and the like. Particularly preferred A' and A" hydrocarbylsand silahydrocarbyls include methylcyclopentadienyl, indenyl, 4,5,6,7tetrahydroindenyl, and trimethylsilanylcyclopentadienyl.

S' is a bridge having a chain length of 1-6 atoms, preferably 1-4 atoms,and especially 1-3 atoms. The bridge must contain at least one siliconatom, but may be composed entirely of silicon atoms. The bridge atomsmay also include 0-2 oxygen atoms and 0-4 carbon atoms. The silicon andcarbon atoms may be unsubstituted or substituted with 1-2 alkyl, silanylor silaalkyl groups which may be the same or different. Preferably, thesilicon atoms are disubstituted with alkyl groups. Thus, preferredbridges include dialkylsilanylene[R₂ Si=], 1-sila-1,1-dialkylethylene[--SiR₂ CH₂ --], tetraalkyldisilanylene [--SiR₂ --SiR₂ --],2-sila-2,2-dialkylpropylene [--H₂ C--SiR₂ --CH₂ --],1,3-disila-1,1,3,3-tetraalkylpropylene [--SiR₂ --CH₂ --R₂ Si--],dialkylsiloxy (dialkyl) silanylene [--R₂ SiO--SiR₂ --],1,4-disila-1,1,4,4-tetraalkylbutylene [--SiR₂ --CH₂ --CH₂ --SiR₂ --].Specifics representative examples include dimethylsilanylene,tetramethyldisilanylene, hexamethyltrisilanylene,1-sila-1,1-dimethylethylene, 2-sila-2,2-dimethylpropylene,1,3-disila-1,1,3,3-tetramethylpropylene, dimethylsiloxy (dimethyl)silanylene, 1,4-disila-1,1,4,4-tetramethylbutylene and the like.

It is critical for catalytic stereospecificity in olefin polymerizationthat these metallocene catalyst be chiral. It is also important that thedegree of rotational restriction of the metallocene portion of thecatalyst be somewhat limited, and that the non-metallocene binding sitesbe constant relative to the metallocene binding site. This is generallyachieved by the silicon-containing bridges of the present catalyst. Forexample, the ring centroid-metal-ring centroid angle for dimethylsilanylbridged bis(4,5,6,7-tetrahydroindenyl) zirconium chloride is 126.4degrees. However, the same angle for the corresponding ethylene bridgedmetallocene is 125.0 degrees, suggesting that the silicon bridge is lessrestrictive than the two-carbon ethylene bridge. Quite surprisingly, thesilicon bridged metallocene polymerizes with a higher stereoregularitythan the ethylene bridged analogue.

The effects of the ring rotational flexibility on the mobility of chiralgroups relative to the metal atom are illustrated in FIGS. 5-8 for C₁-C₄ bridged bis(methylcyclopentadienyl) metallocenes. It is seen thatgenerally, with carbon bridges, the mobility, and hence the incidence ofinversions in stereoregular polymerization, increases with the bridgelength. With C₄ bridges, it is expected that a fairly high proportion ofthe polymer obtained with metallocenes containing them will be atactic.Additionally, as disclosed in Soga et al., Makromol. Chem., RapidCommun. 8, 305-310 (1987), ethylene bridged tetrahydroindenyl zirconiumcatalysts introduce 1-3 insertion of the monomer.

Preferred metallocene catalysts according to the present inventioninclude: racemic [1,1'-dimethylsilanylene-bis(3-methylcyclopentadienyl)]zirconium dichloride; [1,1'-dimethylsilanylene-bis(indenyl)] zirconiumdichloride; [1,1'-dimethylsilanylene-bis(4,5,6,7-tetrahydroindenyl)]zirconium dichloride;[1,1'-(1,1,2,2-tetramethyldisilanylene)-bis(3-methylcyclopentadienyl)]zirconium dichloride;[1,1'-(1,1,2,2-tetramethyldisilanylene)-bis(4,5,6,7-tetrahydroindenyl)]zirconium dichloride;[1,1'-dimethylsilanylene-bis(3-trimethylsilanylcyclopentadienyl)]zirconium dichloride;[1,1'-(1,1,2,2-tetramethyldisilanylene)-bis(3-trimethylsilanylcyclopentadienyl)]zirconium dichloride;[1,1'-(1,1,3,3-tetramethyldisiloxanylene)-bis(4,5,6,7-tetrahydroindenyl)]zirconium dichloride;[1,1'-(1,1,4,4-tetramethyl-1,4-disilanylbutylene)-bis(4,5,6,7-tetrahydroindenyl)]zirconium dichloride;[1,1'-(2,2-dimethyl-2-silapropylene)-bis(3-methylcyclopentadienyl)]zirconium dichloride.

Preferred metallocene catalysts according to the present invention alsoinclude: racemic [1,1'-dimethylsilanylene-bis(3-methylcyclopentadienyl)]hafnium dichloride; [1,1'-dimethylsilanylene-bis(indenyl)] hafniumdichloride; [1,1'-dimethylsilanylene-bis(4,5,6,7-tetrahydroindenyl)]hafnium dichloride;[1,1'-(1,1,2,2-tetramethyldisilanylene)-bis(3-methylcyclopentadienyl)]hafnium dichloride;[1,1'-(1,1,2,2-tetramethyldisilanylene)-bis(4,5,6,7-tetrahydroindenyl)]hafnium dichloride;[1,1'-dimethylsilanylene-bis(3-trimethylsilanylcyclopentadienyl)]hafnium dichloride;[1,1'-(1,1,2,2-tetramethyldisilanylene)-bis(3-trimethylsilanylcyclopentadienyl)]hafnium dichloride;[1,1'-(1,1,3,3-tetramethyldisiloxanylene)-bis(4,5,6,7-tetrahydroindenyl)]hafnium dichloride;[1,1'-(1,1,4,4-tetramethyl-1,4-disilanylbutylene)-bis(4,5,6,7-tetrahydroindenyl)]hafnium dichloride;[1,1'-(2,2-dimethyl-2-silapropylene)-bis(3-methylcyclopentadienyl)]hafnium dichloride.

The silicon bridged metallocenes of the present invention are generallyprepared by first building the ligand structures through simplealkylation/silanylation steps, and then inserting the transition metalusing the metal tetrahalide. Lithium and sodium alkyls are preferablyused for alkylation/silanylation. This is in contrast to Grignardreagents which must generally be employed for alkylene bridges, such asin the preparation of 1,2-ethylene bridged metallocenes, to obtainreasonable yields of the alkylene bridged metallocenes. For example,indene or cyclopentadiene are reacted with alkyllithium such asmethyllithium or butyllithium, in a suitable solvent, such astetrahydrofuran, to form the corresponding alkyllithium indenide orcyclopentadienide. If an alkylated ligand is desired, the alkyllithiumcompound can then be reacted with a corresponding alkylhalide to yieldthe alkylated ligand. For example, n-butylchloride may be reacted withlithium indenide to yield n-butyl indene, and methylchloride withlithium cyclopentadienide to yield methylcyclopentadiene. Silanylationmay be accomplished in an analogous manner, such as by reactingtrimethylchlorosilane with lithium cyclopentadienide to yieldtrimethylsilanyl cyclopentadiene.

Bridge formation also preferably employs alkyllithium or sodiumintermediates rather than Grignard reagents. For example,dimethylsilanylene bridges are formed by the reaction of lithiumindenide, methylcyclopentadienide or trimethylsilanylcyclopentadienide,with dimethyldichlorosilane; and 2-sila-2,2-dimethylpropylene bridges bythe reaction of lithium indenide, methylcyclopentadienide ortrimethylsilanylcyclopentadienide, with di(chloromethyl) dimethylsilane.The bridge formation may also be completed beforealkylation/silanylation, as the order thereof is not generally critical.

Following formation of the desired silicon bridged ligand structure, themetallocene is formed by reaction of the lithium or sodium salt of theligand structure with the transition metal halide, for example,zirconium or hafnium tetrachloride. The racemic form may then generallybe readily separated from the meso form by crystallization from asolvent such as methylene dichloride using a hydrocarbon diluent, e.g.pentane, as an antisolvent, and recovering the crystallized racemicmetallocene by filtration from the solution in which the mesometallocene generally remains soluble.

The silicon bridged metallocenes described herein generally have utilityin stereregular polymerization of α-olefins. The metallocenes may beused alone, but preferably are complexed with an alumoxane cocatalyst ofthe formulae (R'"--Al--O)_(p) for cyclic alumoxanes, orR'"(R'"--Al--O)_(q) AlR₂ " for linear alumoxanes, in which R'" is C₁ -C₅alkyl, for example, methyl, ethyl, propyl, butyl or pentyl, and p and qare integers from 2 to about 25. Most preferably, R'" is methyl and pand q are at least 4. Alumoxanes can be prepared by various proceduresknown in the art. For example, an aluminum alkyl may be treated withwater contained in a moist inert organic solvent, or it may be contactedwith a hydrated salt, such as hydrated ferrous sulfate suspended in aninert organic solvent, to yield an alumoxane. Generally, howeverprepared, the reaction of an aluminum alkyl with a stoichiometric amountof water yields a mixture of the linear and cyclic species of thealumoxane.

The catalyst desirably is in a form of a complex formed upon admixtureof the metallocene as specified with an alumoxane. The catalyst complexmay be prepared as a homogeneous catalyst by addition of the requisitemetallocene and alumoxane to the solvent in which polymerization will becarried out by solution polymerization procedures. The catalyst complexcan also be prepared and employed as a heterogeneous catalyst byadsorbing and complexing the requisite silicon bridged metallocene andalumoxane components on a catalyst support material, such as silica gel,alumina or other inorganic support material. When prepared inheterogeneous or supported form, it is preferred to use silica gel asthe support material. The heterogeneous form of the catalyst complex isgenerally employed in a suspension or slurry polymerization procedurewith or without additional alumoxane present in the liquid phase. In thepreparation of poly-α-olefins, it is preferred to utilize the α-olefinmonomer in liquified state as the polymerization diluent.

The support material for preparing a heterogeneous catalyst may be anyfinely divided inorganic solid porous support, such as talc, silica,alumina, silica-alumina and mixtures thereof. Other inorganic oxidesthat may be employed either alone or in combination with silica orsilica-alumina are magnesia, titania, zirconia, and the like. Thepreferred support material is a silica gel.

The metallocene and alumoxane may be utilized in olefin polymerizationin the form of a heterogeneous supported catalyst by deposition on asupport material, such as silica gel. While it should not be construedthat the invention is limited in any way by the following mechanisticinterpretation, it is considered that for optimal effectiveness of thedeposited alumoxane, it is desirable that the unbound water initiallypresent on the undehydrated silica should be essentially wholly removed,while retaining a portion of surface hydroxyl groups which are capableof reacting with the alumoxane and bonding it to the silica surface. Thesilica gel may be prepared in dehydrated form by heating or otherwisetreating it to remove its water content so as to convert same to aderivate which is clement to the formation the metallocene alumoxanecatalyst complex. A suitable silica gel would have a particle diameterin the range 10-600 microns, preferably 30-100 microns; a surface areaof 50-1000 m² /g, preferably 100-500 m² /g; and a pore volume of 0.5-3.5cm³ /g. The silica gel may be heat treated at 100°-1000° C., preferably200°-800° C. for a period of 1-100 hours, preferably 3-24 hours, toensure removal of unbound water from its surfaces.

The order of addition of the metallocene and alumoxane to the supportmaterial can vary. For example, the metallocene (dissolved in a suitablehydrocarbon solvent) can be first added to the support material followedby the addition of the alumoxane; the alumoxane and metallocene can beadded to the support material simultaneously; the alumoxane can be firstadded to the support material followed by the addition of themetallocene.

The treatment of the support material, as mentioned above, is conductedin an inert solvent. The same inert solvent or a different inert solventcan be employed to dissolve the metallocene and alumoxanes. Preferredsolvents include mineral oils and the various hydrocarbons which areliquid at reaction temperatures and in which the individual adsorbatesare soluble. Illustrative examples of useful solvents include alkanessuch as pentane, iso-pentane, hexane, heptane, octane and nonane;cycloalkanes, such as cyclopentane and cyclohexane; and aromatics suchas toluene, xylenes, ethylbenzene and diethylbenzene. The supportmaterial may be present by itself, which is preferred, or may beslurried in the inert solvent, and the metallocene and alumoxane aredissolved in the inert solvent prior to addition to the supportmaterial.

The supported catalyst is prepared by simply adding the adsorbates in asuitable solvent, preferably toluene, to the support material which isby itself or in a slurry. Preferably, a solution of the adsorbate isadded to the dried support material. Most preferably, a toluene solutionof the adsorbate is added to silica. In accordance with the preferredembodiment of this invention, the alumoxane dissolved in toluene isadded to the silica particles in a first step, and the treated solid isdried. The dried solid is then treated with a solution in an inertsolvent of the metallocene as a second step. In both of these steps, theconditions for addition of the adsorbates are not particularly critical.The adsorbates can be added to the reaction vessel rapidly or slowly.The amount of solvent to be employed is not critical. Nevertheless, theamount should be employed so as to provide adequate heat transfer awayfrom the catalyst components during reaction and to permit good mixing.The temperature maintained during the contact of the reactants can varywidely, such as, from 0° to 100° C. Greater or lesser temperatures canalso be employed. Preferably, the alumoxanes and metallocene are addedto the silica at room temperature. The reaction between the alumoxaneand the support material is rapid, however, it is desirable that thealumoxane be contacted with the support material for about one half hourup to eighteen hours or greater. Preferably, the reaction is maintainedfor about one hour.

At all times, the individual ingredients as well as the recoveredcatalyst components are protected from oxygen and moisture. Therefore,the reactions must be performed in an oxygen and moisture freeatmosphere and recovered in an oxygen and moisture free atmosphere.Preferably, therefore, the reactions are performed in the presence of aninert dry gas, such as nitrogen. The recovered solid catalyst ismaintained in a nitrogen atmosphere.

Upon completion of the reaction of the metallocene and alumoxane withthe support, the solid material can be optionally treated with a smallamount of monomer, e.g. ethylene, to prepolymerize the solid catalystmaterials to a weight increase of from about 50 to about 1000% based ontotal weight of catalyst and support material. Then the solid material,as such or as prepolymerized, can be recovered by any well-knowntechnique. For example, the solid catalyst material can be recoveredfrom the liquid by vacuum evaporation or decantation. The solid isthereafter dried under a stream of pure dry nitrogen or dried undervacuum. Prepolymerization of the solid catalyst material aids inobtaining a polymer produced therefrom in well defined particle form.

The catalyst complex obtained through contacting of the metallocene andthe alumoxane cocatalyst may be homogeneous, heterogeneous or supportedand may be formed prior to introduction of these components into thereactor. The homogeneous catalyst may be formed in the reactor. Theratio of Al to transition metal can be in the range of 0.5-100,000, mostdesirably 1-1000. The preferred ratio of Al to metal is in the range1-200, desirably 20-200. If desired, the heterogeneous and supportedcatalyst complex may be contacted with a small amount of a monomer, e.g.ethylene, in amounts such as to effect a weight gain of 50-1000% basedon total weight of catalyst and support material, if employed. In thiscase, additional alumoxane cocatalyst may be used in the reactor so thatthe total ratio of Al to metal is in the range 1-5000, preferably 5-4000and most preferably 10-1000. Likewise, in this case, a small amount ofanother aluminum compound may be added to the reactor together with, orinstead of, additional alumoxane, for the purposes of scavenging anyimpurities which may be present in the reactor.

In accordance with a preferred procedure the metallocene-alumoxanecatalyst complex may be used to produce isotactic poly-α-olefins byslurry polymerization utilizing the olefin monomer as the polymerizationdiluent in which a metallocene-alumoxane catalyst complex is dissolvedin an amount sufficient to yield a polymer with the desired monomercontent. If desired, comonomer is supplied to the polymerizationdiluent. Generally the polymerization process is carried out with apressure of from about 10 to about 1000 psi, most preferably from about40 to about 600 psi. The polymerization diluent is maintained at atemperature of from about -10 to about 150° C., preferably from about 20to about 100° C., and most preferably from about 30 to about 90° C.These catalysts may also be employed in a high temperature/pressurepolymerization process. In such, the pressure can be in the range of5,000-40,000 psi and the temperature in the range of 120°-300° C.

The polymerization may be carried out as a batchwise slurrypolymerization or as a continuous process slurry polymerization. Theprocedure of continuous process slurry polymerization is preferred, inwhich event α-olefin and catalyst are continuously supplied to thereaction zone in amounts equal to the α-olefin and catalyst removed fromthe reaction zone with the polymer in the product stream.

The preparation of silicon bridged metallocenes of the presentinvention, and the use thereof as α-olefin polymerization catalysts, areillustrated by way of the examples which follow.

EXAMPLE 1

The compound 1,1'-dimethylsilanylene bridged bis(indenyl) zirconiumdichloride was prepared, and the racemic isomers thereof separated fromthe meso isomer. In a nitrogen atmosphere, 44 ml indene and 150 mltetrahydrofuran (THF) were magnetically stirred in a one-liter flask.Carefully, 215 ml of methyllithium (1.4M in THF) was added thereto withstirring at 0° C., and stirred for one hour. In another one-liter flask,22.4 ml dimethyldichlorosilane and 150 ml THF were stirred, and themethyllithium indenide solution slowly added thereto at 25° C. over aone hour period. The mixture was stirred for one additional hour andthen evaporated to one-half volume using a rotary evaporator. Carefully,225 ml of methyllithium (1.4M in THF) was added thereto at 0° C. and themixture stirred for one hour at 25° C.

In another one-liter flask, 200 cc THF was cooled to -80° C. and 40 g ofzirconium tetrachloride was slowly added with stirring. The stirringsolution was allowed to warm to 25° C. The indene solution was slowlypoured into the zirconium halide solution over a period of one hour at25° C. and stirred overnight. The mixture was evaporated to an oil usinga vacuum evaporator and allowed to stand for 24 hours. The oily mixturewas filtered through a coarse glass frit to obtain the yellowcrystalline, racemic bridged indene complex. The complex was washed withseveral 10 cc portions of THF which was at -20° C. The meso isomer wasobtained by extracting the vacuum evaporated filtrate withdichloromethane. To obtain the tetrahydroindenyl derivative, 200 cc ofmethylene chloride and 500 mg of platinum black or platinum (IV) oxidewas added to the yellow racemic solid. This mixture was hydrogenated at45° C. in a steel vessel using 600 psig hydrogen pressure for fourhours. The resultant solution was filtered and evaporated to 100 cc orless. The insoluble racemic isomer was filtered off while the solutionwas slowly evaporated with cooling. The racemic isomer was thuscrystallized in high purity. The yield was approximately 20 g of theracemic tetrahydroindenyl isomer. The crystal structure of this isomeris given in FIG. 10. The H-1 NMR spectrum of the racemic isomer indeuterobenzene, FIG. 9, showed the following main resonances:

singlet, 6H, 0.35δ

doublets, 4H, 5.2δ, 6.7δ

multiplets, 16H, 1.4δ, 1.9δ, 2.2δ, 2.6δ, 3.1δ

The H-1 NMR spectrum of the racemic isomer in deuterobenzene prior tohydrogenation, (CH₃)₂ Si(indenyl)₂ ZrCl₂, showed the followingresonances:

singlet, 6H, 0.55δ

doublets, 4H, 5.8δ, 6.8δ

multiplets, 8H, 6.8δ, 7.1-7.4δ

EXAMPLE 2

The compound 1,1'-dimethylsilanylene bridgedbis(3-methylcyclopentadienyl) zirconium dichloride was prepared. In anitrogen atmosphere, 28 g methylcyclopentadiene monomer and 150 cctetrahydrofuran were magnetically stirred in a one-liter flask. 250 ccmethyllithium (1.4M) was carefully added with stirring at 0° C. for onehour. In another one-liter flask, 22.6 g dimethyldichlorosilane and 150cc THF were stirred, the lithium methylcyclopentadienide solution wasslowly added to the silane solution at 25° C. over a one hour period andstirred for one additional hour. The solution was evaporated to one-halfvolume using a rotary evaporator, and then 250 cc of methyllithium(1.4M) at 0° C. was carefully added and stirred for one hour at 25° C.In another one-liter flask, 200 cc THF was cooled to -80° C. and 40.8 gof zirconium tetrachloride was slowly added with stirring. The stirringsolution was allowed to warm to 25° C. The lithiumdimethylsilanyldi(methylcyclopentadienide) solution was slowly pouredinto the zirconium halide solution over a period of one hour at 25° C.and stirred 12 hours. The mixture was evaporated to an oil using avacuum evaporator. The residue was extracted with hot hexane to dissolvethe bridged metallocene dichloride (CH₃)₂ Si(CpMe)₂ ZrCl₂. The insolublesalts were filtered from the solution of metallocene. The hexane wascooled and evaporated to obtain 40 g of crystalline metallocene productwhich was stored in a dry, inert atmosphere. The H-1 NMR indicated thatthe product was a mixture of the meso and racemic isomers which could beseparated by fractional crystallization from hexane. The NMR indeuterobenzene showed the following resonances:

Racemic and meso isomers:

singlets, 12H, 0.2δ, 2.3δ

multiplets, 6H, 5.0δ, 5.2δ, 5.4δ, 5.6δ, 6.5δ, 6.6.δ

Isolated racemic isomer:

singlets, 12H, 0.2δ, 2.3δ

multiplets, 6H, 5.0δ, 5.6δ, 6.6δ

EXAMPLE 3

The compound 1,1'-dimethylsilanylene bridgedbis(3-trimethylcyclopentadienyl) zirconium dichloride was prepared. In anitrogen atmosphere, 48.4 g 2,4-cyclopentadien-1-yltrimethyl silane(Aldrich Chemical Co.) and 150 cc tetrahydrofuran in a one-liter flaskwere magnetically stirred. 250 cc methyllithium (1.4M) was carefullyadded with stirring at 0° C. for one hour. In another one-liter flask,22.6 g dimethyldichlorosilane and 150 cc THF were stirred, and thelithium trimethylcyclopentadienide solution was slowly added to thedichlorosilane solution at 25° C. over a one hour period and stirred forone additional hour. The solution was evaporated to one-half volumeusing a rotary evaporator, and then 250 cc of methyllithium (1.4M) at 0°C. was carefully added and stirred for one hour at 25° C. In anotherone-liter flask, 200 cc THF was cooled to -80° C. and 40.8 g ofzirconium tetrachloride was slowly added with stirring. The stirringsolution was allowed to warm to 25° C. The ligand solution was slowlypoured into the zirconium halide solution over a period of one hour at25° C. and stirred overnight. The mixture was evaporated to an oil usinga vacuum evaporator. The residue was extracted with hot hexane todissolve the bridged metallocene dichloride (CH₃)₂ Si(Cp-Si(CH₃)₃)₂ZrCl₂. The insoluble salts were filtered from the solution ofmetallocene. The hexane was cooled and evaporated to obtain 68 g ofcrystalline metallocene product which was stored in a dry, inertatmosphere. The H-1 NMR indicated that the product of the reaction was amixture of the meso and racemic isomers which could be separated byfractional crystallization from hexane. The NMR in deuterobenzene showedthe following resonances:

Racemic and meso isomers:

singlets, 24H, 0.3δ, 0.4δ, 0.5δ

multiplets, 6H, 5.65δ, 5.8δ, 5.9δ, 6.1δ, 6.95δ, 7.1δ

Isolated racemic isomer:

singlets, 24H, 0.3δ, 0.5δ:

multiplets, 6H, 5.65δ, 6.1δ, 7.1δ

EXAMPLE 4

The compound 1,1'-diethylsilanylene bridgedbis(3-isobutylcyclopentadienyl) zirconium dichloride was prepared. In anitrogen atmosphere, 42.7 g isobutylcyclopentadiene monomer and 150 cctetrahydrofuran were magnetically stirred in a one-liter flask.Isobutycyclopentadiene monomer can be prepared by reacting sodiumcyclopentadienide with isobutylbromide in THF at 40° C. for two hours.250 cc methyllithium (1.4M) was carefully added with stirring at 0° C.for one hour. In another one-liter flask, 27.5 g diethyldichlorosilaneand 150 cc THF were stirred, and the lithium isobutylcyclopentadienidesolution was slowly added to the silane solution at 25° C. over a onehour period and stirred for one additional hour. The solution wasevaporated to one-half volume using a rotary evaporator, and then 250 ccof methyllithium (1.4M) at 0° C. was carefully added and stirred for onehour at 25° C. In another one-liter flask, 200 cc THF was cooled to -80°C. and 40.8 g of zirconium tetrachloride was slowly added with stirring.The stirring solution was allowed to warm to 25° C. The ligand solutionwas slowly poured into the zirconium halide solution over a period ofone hour at 25° C. and stirred overnight. The mixture was evaporated toan oil using a vacuum evaporator. The residue was extracted with hothexane to dissolve the bridged metallocene dichloride (CH₃ --CH₂)₂Si(Cp--CH₂ CH(CH₃)₂)₂ ZrCl₂. The insoluble salts were filtered from thesolution of metallocene. The hexane was evaporated to obtain 52 g of thenon-crystalline metallocene product which was stored in a dry, inertatmosphere. The H-1 NMR indicated that the product of the reaction was amixture of the meso and racemic isomers. The NMR in deuterobenzeneshowed the following resonances:

Racemic and meso isomers:

multiplet, 10H, 0.8δ

multiplet, 12H, 0.9δ

multiplet, 2H, 1.7δ

multiplet, 4H, 2.6δ

multiplet, 6H, 5.3-6.7δ

EXAMPLE 5

A single stereoisomer of[1,1'-(2,2-dimethyl-2-silapropylene)-bis(3-trimethylsilanylcyclopentadienyl)]zirconiumdichloride, (CH₃)₂ Si(CH₂)₂ (C₅ H₃ Si(CH₃)₃)₂ ZrCl₂ was prepared andseparated. In a nitrogen atmosphere, 100 cc distilled tetrahydrofuran,28 cc of 1.8M sodium cyclopentadienide solution (THF), and 3.65 cc ofdi(chloromethyl)-dimethylsilane were combined and stirred for 24 hoursat 35° C. 36 cc of 1.4M methyllithium at 0° C. was slowly added andallowed to warm to 25° C. while stirring for one hour. 6.4 cc oftrimethylchlorosilane at 25° C. was added and stirred for one hour. 40cc of 1.4M methyllithium at -20° C. was added, stirred and allow to warmto 25° C. The solution was cooled to -20° C. and 11 g of zirconiumtetrachloride was slowly added. The solution was allowed to warm to 25°C. and stirred for 12 hours. The mixture was evaporated to dryness invacuo, then 200 cc methylene dichloride was added and stirred. Dry HClgas was bubbled into the solution for five minutes, then excess HCl waspurged out by bubbling with nitrogen. The solution was filtered througha medium fritted glass filter. The solution was evaporated to 100 cc orless and cooled. Pentane was added, and the crystalline solid wasseparated. The filtrate may be concentrated to an oil to recover theother isomer. The yield was 6 grams of a crystalline isomer, possiblythe racemic one, and 10 grams of an impure oil containing the otherisomer. The crystalline isomer did not crystallize in a form adequatefor x-ray structure determination. The H-1 NMR of the crystalline isomerin CDCl₃ showed the following resonances:

singlets, 24H, 0.3δ, 0.4δ

doublet, 2H, 5.85δ

multiplets, 4H, 1.7δ, 2.15δ 4H, 6.35δ, 6.5-6.6δ

EXAMPLE 6

A tetramethylsilanylene bridged bis(methylcyclopentadienyl) zirconiumdichloride was prepared. In a nitrogen atmosphere, 28 gmethylcyclopentadiene monomer and 150 cc tetrahydrofuran (THF) weremagnetically stirred in a one liter flask. 250 cc methyllithium (1.4M inTHF) was added carefully with stirring at 0° C., and stirred for onehour. In another one liter flask, 32.9 g,1,1,2,2-tetramethyldichlorodisilane (Petrarch Chem. Co.) and 150 cc THFwere stirred, and the lithium methylcyclopentadienide solution wasslowly added to the silane solution at 25° C. over a one hour period.The mixture was stirred for one additional hour. The solution wasevaporated to one-half volume using a rotary evaporator, and then 250 ccof methyllithium (1.4M) was carefully added at 0° C. This was stirredfor one hour at 25° C.

In another one liter flask, 200 cc THF was cooled to -80° C. and 40.8 gof zirconium tetrachloride was slowly added with stirring. The stirringsolution was allowed to warm to 25° C. The ligand solution was slowlypoured into the zirconium halide solution over a period of one hour at25° C., and stirred for 12 hours. The mixture was evaporated to an oilusing a vacuum evaporator. The residue was extracted with hot hexane todissolve the bridged metallocene dichloride (CH₃)₄ Si₂ (C₅ H₃ CH₃)₂ZrCl₂. This was filtered to separate the insoluble salts from thesolution of metallocene. The hexane was cooled and evaporated to obtain45 g of a semi-crystalline metallocene product. The product was storedin a dry, inert atmosphere. The H-1 NMR indicated that the product was amixture of the meso and racemic isomers which were not separated. TheNMR spectrum in deuterobenzene showed the following resonances:

Racemic and meso isomers:

singlets, 12H, 0.25δ 6H, 2.25δ, 2.35δ

multiplets, 6H, 6.15δ, 6.35δ

EXAMPLE 7

The compound tetramethyldisiloxane bridged bis(tetrahydroindenyl)zirconium dichloride was prepared. In a nitrogen atmosphere, 44 ccindene and 150 cc tetrahydrofuran were magnetically stirred in a oneliter flask. 250 cc methyllithium (1.4M) were added with stirring at 0°C., and stirred for one hour. In another one liter flask, 35.5 g1,3-dichlorotetramethyldisiloxane (Petrarch Chemical Co.) and 150 cc THFwere stirred and the lithium idenide solution was slowly added to thesiloxane solution at 25° C. over a one hour period. The mixture wasstirred for one additional hour. The solution was evaporated to one-halfvolume using a rotary evaporator, and then 250 cc of methyllithium(1.4M) was carefully added at 0° C. The mixture was stirred for one hourat 25° C.

In another one liter flask, 200 cc THF was cooled to -80° C., and 40.8 gof zirconium tetrachloride was slowly added with stirring. The stirringsolution was allowed to warm to 25° C. The ligand solution was slowlypoured into the zirconium halide solution over a period of one hour at25° C., and stirred 12 hours. The mixture was evaporated to an oil usinga vacuum evaporator. The residue was extracted with dichloromethane todissolve the bridged indene metallocene dichlorides (CH₃)₄ Si₂ O(C₉ H₆)₂ZrCl₂, and filtered to separate the insoluble salts from the solution ofmetallocene. The dichloromethane was cooled and evaporated to obtain 45g of a semi-crystalline metallocene product, which was stored in a dry,inert atmosphere.

To obtain the tetrahydroindenyl derivative, 200 cc of dichloromethaneand 500 mg of platinum black or platinum (IV) oxide was added to theyellow semi-crystalline product. This mixture was hydrogenated at 45° C.in a steel vessel using 600 psig hydrogen pressure for four hours. Theresultant solution was filtered and evaporated to 100 cc or less. Theinsoluble racemic isomer was filtered off while slowly evaporating thesolution. The racemic isomer [[(C₉ H₁₀)Si(CH₃)₂ ]₂ O]ZrCl₂, verified bysingle crystal x-ray determination, was thus crystallized in highpurity. The H-1 NMR spectrum of the racemic isomer in deuterobenzeneshowed the following resonances:

singlets, 12H, 0.3δ

doublets, 4H, 6.2δ, 6.6δ

multiplets, 16H, 1.45δ, 2.0δ, 2.2δ, 2.55δ, 3.0δ

EXAMPLE 8

The compound tetramethyldisiloxane bridged bis(cyclopentadienyl)zirconium dichloride was prepared. In a nitrogen atmosphere, 23.1 gcyclopentadiene monomer and 150 cc tetrahydrofuran were magneticallystirred in a one liter flask. 250 cc methyllithium (1.4M) was carefullyadded with stirring at 0° C., and stirred for one hour. In another oneliter flask, 35.5 g [1,3-dichlorotetramethyldisiloxane] (Petrarch Chem.Co.) and 150 cc THF were stirred, and the lithium cyclopentadienidesolution was slowly added to the silane solution at 25° C. over a onehour period. The mixture was stirred for one additional hour. Thesolution was evaporated to one-half volume using a rotary evaporator,and then 250 cc of methyllithium (1.4M) was carefully added at 0° C.This was stirred for one hour at 25° C.

In another one liter flask, 200 cc THF was cooled to -80° C., and 40.8 gof zirconium tetrachloride was slowly added with stirring. The stirringsolution was allowed to warm to 25° C. The ligand solution was slowlypoured into the zirconium halide solution over a period of one hour at25° C., and stirred for 12 hours. The mixture was evaporated to an oilusing a vacuum evaporator. The residue was extracted with hot hexane todissolve the bridged metallocene dichloride (CH₃)₄ Si₂ O(C₅ H₄)₂ ZrCl₂.This was filtered to separate the insoluble salts from the solution ofmetallocene. The hexane was cooled and evaporated to obtain 42 g of asemi-crystalline metallocene product. The product was stored in a dry,inert atmosphere. The NMR spectrum in deuterobenzene showed thefollowing resonances:

singlets, 12H, 0.3δ

multiplets 8H, 6.35δ, 6.5δ

EXAMPLE 9

The compound 1,1,4,4-tetramethyl-1,4-disilabutylene bridgedbis(methylcyclopentadienyl) zirconium dichloride was prepared. In anitrogen atmosphere, 23.1 g cyclopentadiene monomer and 150 cctetrahydrofuran were magnetically stirred in a one-liter flask. 250 ccmethyllithium (1.4M) was carefully added with stirring at 0° C., andstirred for one hour. In another one-liter flask, 37.7 g1,1,4,4-tetramethyl-1,4-dichlorodisilaethylene (Petrarch Chem. Co.) and150 cc THF were stirred, and the lithium methylcyclopentadienidesolution was slowly added to the silane solution at 25° C. over a onehour period. The mixture was stirred for one additional hour. Thesolution was evaporated to one-half volume using a rotary evaporator,and then 250 cc of methyllithium (1.4M) was carefully added at 0° C.This was stirred for one hour at 25° C.

In another one-liter flask, 200 cc THF was cooled to -80° C., and 40.8 gof zirconium tetrachloride was slowly added with stirring. The stirringsolution was allowed to warm to 25° C. The ligand solution was slowlypoured into the zirconium halide solution over a period of one hour at25° C., and stirred for 12 hours. The mixture was evaporated to an oilusing a vacuum evaporator. The residue was extracted with hot hexane todissolve the bridged metallocene dichloride (CH₂)₂ (CH₃)₄ Si₂ (C₅ H₄)₂ZrCl₂. This was filtered to separate the insoluble salts from thesolution of metallocene. The hexane was cooled and evaporated to obtain55 g of a semi-crystalline metallocene product. The product was storedin a dry, inert atmosphere. The NMR spectrum in deuterobenzene showedthe following resonances:

singlets, 12H, 0.15δ 4H, 0.75δ

multiplets, 8H, 6.35δ, 6.45δ

EXAMPLE 10

The compound dimethylsilanylene bridged bis(methylcyclopentadienyl)hafnium dichloride was prepared. In a nitrogen atmosphere, 28 gmethylcyclopentadiene monomer and 150 cc diethylether were magneticallystirred in a one liter flask. 250 cc methyllithium (1.4M) was carefullyadded with stirring at 0° C. and stirred for one hour. In another oneliter flask, 22.4 cc dimethyldichlorosilane 150 and 150 cc diethyletherwere stirred and the lithium methylcyclopentadienide solution was slowlyadded to the silane solution at 25° C. over a one hour period andstirred for one additional hour. The solution was evaporated to one-halfvolume using a rotary evaporator, and then 250 cc of methyllithium(1.4M) at 0° C. was carefully added and stirred for one hour at 25° C.The ether solvent was evaporated completely using a vacuum evaporator.400 cc toluene and 56.0 g hafnium tetrachloride was added. The flask wasattached to a reflux condenser and nitrogen bubbler, and the toluenesolution was refluxed for 24 hours under a nitrogen atmosphere. Thetoluene solution was cooled to 25° C. and vacuum evaporated to dryness.The residue containing the metallocene complex was extracted from theunreacted salts by washing with 500 cc dichloromethane. Thedichloromethane solution was evaporated to obtain 30 g of the racemicisomer, rac-(CH₃)₂ Si(C₅ H₃ CH₃)₂ HfCl₂, as a crystalline product. TheH-1 NMR spectrum in deuterobenzene showed the following resonances:

isolated racemic isomers;

singlets, 12H, 0.25δ, 2.35δ

multiplets, 6H, 5.15δ, 5.7δ, 6.6δ

racemic and meso isomers;

singlets, 12H, 0.25δ, 2.35δ

multiplets, 6H, 5.1δ, 5.2δ, 5.4δ, 5.7δ, 6.5δ, 6.6δ

EXAMPLE 11

The compound dimethylsilanylene bridged bis(indenyl) hafnium dichloridewas prepared. In a nitrogen atmosphere, 44 cc indene and 150 ccdiethylether were magnetically stirred in a one-liter flask. 250 ccmethyllithium (1.4M) was carefully added with stirring at 0° C. andstirred for one hour. In another one-liter flask, 22.4 ccdimethyldichlorosilane 150 and 150 cc diethylether were stirred and thelithium indene solution was slowly added to the silane solution at 25°C. over a one hour period and stirred for one additional hour. Thesolution was evaporated to one-half volume using a rotary evaporator,and then 250 cc of methyllithium (1.4M) at 0° C. was carefully added andstirred for one hour at 25° C. The ether solvent was evaporatedcompletely using a vacuum evaporator. 400 cc toluene and 56.0 g hafniumtetrachloride was added. The flask was attached to a reflux condenserand nitrogen bubbler, and the toluene solution was refluxed for 24 hoursunder a nitrogen atmosphere. The toluene solution was cooled to 25° C.and vacuum evaporated to dryness. The residue containing the metallocenecomplex was extracted from the unreacted salts by washing with 500 ccdichloromethane. The dichloromethane solution was evaporated to obtain30 g of the racemic isomer, rac-(CH₃)₂ Si(C₉ H₆)₂ HfCl₂, as acrystalline product. The H-1 NMR spectrum in deuterobenzene showed thefollowing resonances:

Isolated racemic isomers:

singlets, 6H, 0.6δ

doublets, 4H, 5.85δ, 6.85δ

multiplets, 8H, 6.80δ, 7.1-7.4δ

POLYMERIZATION EXAMPLES

In the Examples following, the alumoxane employed was prepared by adding45.5 grams of ferrous sulfate heptahydrate in four equally spacedincrements over a two hour period to a rapidly stirred two literround-bottom flask containing one liter of a 10.0 wt. percent solutionof trimethylaluminum (TMA) in hexane. The flask was maintained at 50° C.under a nitrogen atmosphere. Methane produce was continuously vented.Upon completion of the addition of ferrous sulfate heptahydrate, theflask was continuously stirred and maintained at a temperature of 60°for six hours. The reaction mixture was cooled to room temperature andallowed to settle. The clear solution was separated from the solids bydecantation.

Molecular weights were determined on a Water's Associates Model No. 150CGPC (Gel Permeation Chromatograph). The measurements were obtained bydissolving polymer samples in hot trichlorobenzene and filtering. TheGPC runs are performed at 145° C. in trichlorobenzene at 1.0 ml/min flowusing styragel columns from Perkin Elmer, Inc. 300 microliters of a 0.1%solution in trichlorobenzene were injected, and the samples were run induplicate. The integration parameters were obtained with aHewlett-Packard Data Module.

EXAMPLE 12

A one liter stainless steel pressure vessel, equipped with an inclineblade stirrer, an external jacket for temperature control, a septuminlet and vent line and a regulated supply of dry ethylene, propyleneand nitrogen, was cleaned with boiling toluene and dried anddeoxygenated with a nitrogen flow. The reactor temperature was adjustedto 20° C., and 200 cc of distilled, degassed toluene was added. Tenmilliliters of a 0.8M toluene solution of methylalumoxane was injected,and the mixture was stirred at 0 psig under nitrogen. A toluene solution(10 cc) containing 5.00 mg of the racemic isomer of dimethylsilanylenebridged bis tetrahydroindenyl zirconium dichloride, (CH₃)₂ Si(C₉ H₁₀)₂ZrCl₂, was injected. Immediately 100 cc of liquid propylene was added,and the mixture was stirred for two hours at 20° C. The product wasrecovered by rapidly venting and opening the reactor. Residual toluenewas evaporated in a stream of air, and the yield was weighed. Theproduct was analyzed by gel permeation chromatography for molecularweight, by differential scanning calorimetry for melting point and bycarbon-13 nuclear magnetic resonance spectrometry for tacticity. Theresults are given in Table 1.

EXAMPLE 13

The polymerization of this example was performed as in Example 12 exceptthat 5.00 mg of racemic dimethylsilanylene bridged bis (indenyl)zirconium dichloride, (CH₃)₂ Si(C₉ H₆)₂ ZrCl₂, was substituted for themetallocene of Example 12. The results are tabulated in Table 1.

EXAMPLE 14

The polymerization of this example was performed as in Example 12 exceptthat 10.0 mg of racemic dimethylsilanylene bridged bis(methylcyclopentadienyl) zirconium dichloride, (CH₃)₂ Si(C₅ H₃ CH₃)₂ZrCl₂, was substituted for the metallocene of Example 12. The resultsare tabulated in Table 1.

EXAMPLE 15

The polymerization of this example was performed as in Example 12 exceptthat 10.0 mg of racemic dimethylsilanylene bridgedbis(trimethylsilanylcyclopentadienyl) zirconium dichloride, (CH₃)₂ Si(C₅H₃ Si(CH₃)₃)₂ ZrCl₂, was substituted for the metallocene of Example 12.The results are tabulated in Table 1.

EXAMPLE 16

The polymerization of this example was performed as in Example 12 exceptthat 10.0 mg of tetramethyldisilanylene bridgedbis(trimethylsilanylcyclopentadienyl) zirconium dichloride, (CH₃)₄ Si₂(C₅ H₃ Si(CH₃)₃)₂ ZrCl₂, was substituted for the metallocene of Example12. The results are tabulated in Table 1.

EXAMPLE 17

The polymerization of this example was performed as in Example 12 exceptthat 10.0 mg of tetramethyldisilanylene bridgedbis(methylcyclopentadienyl) zirconium dichloride, (CH₃)₄ Si₂ (C₅ H₃CH₃)₂ ZrCl₂, was substituted for the metallocene of Example 12. Theresults are tabulated in Table 1.

EXAMPLE 18

The polymerization of this example was performed as in Example 12 exceptthat 10.0 mg of racemic tetramethyldisiloxane bridgedbis(tetrahydroindenyl) zirconium dichloride, (CH₃)₄ Si₂ O(C₉ H₁₀)₂ZrCl₂, was substituted for the metallocene of Example 12. The resultsare tabulated in Table 1.

EXAMPLE 19

The polymerization of this example was performed as in Example 12 exceptthat 10.0 mg of racemic tetramethyldisilanylene bridgedbis(tetrahydroindenyl) zirconium dichloride, (CH₃)₄ Si₂ (C₉ H₁₀)₂ ZrCl₂,was substituted for the metallocene of Example 12. The results aretabulated in Table 1.

EXAMPLE 20

The polymerization of this example was performed as in Example 12 exceptthat 10.0 mg of 2,2-dimethyl-2-silapropylene bridgedbis(cyclopentadienyl) zirconium dichloride, (CH₃)₂ Si(CH₂)₂ (C₅ H₄)₂ZrCl₂, was substituted for the metallocene of Example 12. The resultsare tabulated in Table 1.

EXAMPLE 21

The polymerization of this example was performed as in Example 12 exceptthat 10.0 mg of said metallocene was used and 100 cc of purified4-methyl-1-pentene was substituted for the propylene of Example 12. Theresults are tabulated in Table 1.

EXAMPLE 22

The polymerization of this example was performed as in Example 12 exceptthat 100 cc of purified 1-octene was substituted for the propylene ofExample 12. The results are tabulated in Table 1.

EXAMPLE 23

The polymerization of this example was performed as in Example 12 exceptthat 5.00 mg of racemic dimethylsilanylene bridged bis(indenyl) hafniumdichloride, (CH₃)₂ Si(C₉ H₆)₂ HfCl₂, was substituted for the metalloceneof Example 12. The results are tabulated in Table 1.

EXAMPLE 24-COMPARATIVE EXAMPLE

The polymerization of this example was performed as in Example 12 exceptthat 15.0 mg of racemic ethylene bridged bis(tetrahydroindenyl)zirconium dichloride rac-(CH₂)₂ (C₉ H₁₀)₂ ZrCl₂, was substituted for themetallocene of Example 12. The results are tabulated in Table 1.

EXAMPLE 25-COMPARATIVE EXAMPLE

The polymerization of this example was performed as in Example 24 exceptthat 10.0 mg of said metallocene was used and the polymerization wasperformed at 50° C. rather than 20° C. The results are tabulated inTable 1.

While an embodiment and application of this invention has been shown anddescribed, it will be apparent to those skilled in the art that manymore modifications are possible without departing from the inventiveconcepts herein described. The invention, therefore, is not to berestricted except as is necessary by the prior art and by the spirit ofthe appended claims.

                                      TABLE I                                     __________________________________________________________________________    Polymerization Results                                                                                                      Melting point,                                                                        Tacticity, %            Example                                                                            Catalyst, mg        Cocatalyst, m moles                                                                      Yield, g                                                                           -- Mw                                                                              °C.                                                                            meso                    __________________________________________________________________________                                                          placements              12   rac-(CH.sub.3).sub.2 Si(C.sub.9 H.sub.10).sub.2 ZrCl.sub.2,                                       methylalumoxane, 8.0                                                                     20.7 85,300                                                                             153.1   98.6                    13   rac-(CH.sub.3).sub.2 Si(C.sub.9 H.sub.6).sub.2 ZrCl.sub.2,                                        methylalumoxane, 8.0                                                                     11.8 73,300                                                                             149.0   97.6                    14   rac-(CH.sub.3).sub.2 Si(C.sub.5 H.sub.3 CH.sub.3).sub.2 ZrCl.sub.2,           10.0                methylalumoxane, 8.0                                                                     50.7 28,000                                                                             139.0   97.3                    15   rac-(CH.sub.3).sub.2 Si(C.sub.5 H.sub.3 Si(CH.sub.3).sub.3).sub.2             ZrCl.sub.2, 10.0    methylalumoxane, 8.0                                                                     48.0 63,000                                                                             142.0   97.5                    16   (CH.sub.3).sub.4 Si.sub.2 (C.sub.5 H.sub.3 Si(CH.sub.3).sub.3).sub.2          ZrCl.sub.2, 10.0    methylalumoxane, 8.0                                                                     26.5 31,500                                                                             108.1   88.2                    17   (CH.sub.3).sub.4 Si.sub.2 (C.sub.5 H.sub.3 CH.sub.3).sub.2 ZrCl.sub.2         , 10.0              methylalumoxane, 8.0                                                                     26.1 20,600                                                                             None    63.9                    18   rac-(CH.sub.3).sub.4 Si.sub.2 O(C.sub.9 H.sub. 10).sub.2 ZrCl.sub.2,          10.0                methylalumoxane, 8.0                                                                      7.7  2,900                                                                             None    62.6                    19   rac-(CH.sub.3).sub.4 Si.sub.2 (C.sub.9 H.sub.10).sub.2 ZrCl.sub.2,            10.0                methylalumoxane, 8.0                                                                      5.9 96,500                                                                             149.0   98.1                    20   (CH.sub.3).sub.2 Si(CH.sub.2).sub.2 (C.sub.5 H.sub.4).sub.2 ZrCl.sub.         2, 10.0             methylalumoxane, 8.0                                                                     24.6 61,200                                                                             None    52.1                    21   rac-(CH.sub.3).sub.2 Si(C.sub.9 H.sub.10).sub.2 ZrCl.sub.2,                                       methylalumoxane, 8.0                                                                     51.3  6,200                                                                              55.0   n.d.                    22   rac-(CH.sub.3).sub.2 Si(C.sub.9 H.sub.10).sub.2 ZrCl.sub.2,                                       methylalumoxane, 8.0                                                                     39.1  5,900                                                                             None    92.0                    23   rac-(CH.sub.3).sub.2 Si(C.sub.9 H.sub.6).sub.2 HfCl.sub.2,                                        methylalumoxane, 8.0                                                                      8.2 550,000                                                                            149.3   98.2                    24   rac-(CH.sub.2).sub.2 (C.sub.9 H.sub.10).sub.2 ZrCl.sub.2,                                         methylalumoxane, 8.0                                                                     53.0 30,400                                                                             141.0   97.3                    25   rac-(CH.sub.2).sub.2 (C.sub.9 H.sub.10).sub.2 ZrCl.sub.2,                                         methylalumoxane, 8.0                                                                     32.5  5,200                                                                             128.7   94.2                    __________________________________________________________________________

I claim:
 1. A process for polymerizing α-olefins, which comprisescontacting alpha-olefins having two or more carbon atoms underpolymerization conditions with a catalyst system; comprising:(a) atransition metal compound represented by formula: ##STR6## wherein M' isa Group IV-B transition metal; X' and X" are the same or differenthydride, halogen, hydrocarbyl or halohydrocarbyl having up to about 6carbon atoms; A' and A" are the same or different asymmetricalmononuclear or polynuclear hydrocarbyl or silahydrocarbyl moieties; andS' is a bridge of 1-4 atoms selected from the group consisting ofsilanylene, silaalkylene, oxasilanylene and oxasilaalkylene; and (b) anorganoaluminum component.
 2. A process for producing poly alpha olefinwhich comprises contacting alpha-olefins having two or more carbon atomsunder polymerization conditions with a catalyst system containing(a) achiral transition metal compound represented by the formula: ##STR7##wherein M' is titanium, zirconium or hafnium; X' and X" are the same ordifferent hydride, chlorine, bromine, iodine, or 1-6 carbon atom alkyl,haloalkyl, aryl or haloaryl; n and m are the same or different integersfrom 1 to 4; R' and R" are the same or different hydrocarbyl orsilahydrocarbyl of 1-20 carbon atoms, and 0-2 silicon atoms, or takentogether, two or more of R' or R" are hydrocarbylene orsilahydrocarbylene of 1-20 carbon atoms and 0-2 silicon atoms; and S' isa chain of 0-4 carbon atoms and 1-2 silicon atoms selected from thegroup consisting of silanylene, silaalkylene, oxasilanylene andoxasilaalkylene, in which each silicon atom is disubstituted with thesame or different hydrocarbyl having 1 to 5 carbon atoms; and (b) anorganoaluminum component.
 3. A process for producing stereo regularpolyalpha-olefins under polymerization conditions comprising contactingalpha-olefins having two or more carbon atoms with:(a) a transitionmetal compound represented by the formula: ##STR8## wherein M' is aGroup IV-B transition metal; X' and X" are the same or differenthydride, halogen, hydrocarbyl or halohydrocarbyl having up to about 6carbon atoms; A' and A" are the same or different asymmetricalmononuclear or polynuclear hydrocarbyl or silahydrocarbyl moieties; andS' is a bridge of 1-4 atoms selected from the group consisting ofsilanylene, silaalkylene, oxasilanylene and oxasilaalkylene and (b) anorganoaluminum component.
 4. The process according to claim 1, 2 or 3wherein the transition metal compound, the organoaluminum component, orboth is on a support.
 5. A process for polymerizing α-olefins whichcomprises contacting alpha-olefins containing two or more carbon atomsunder polymerization conditions with a catalyst system comprising atransition metal compound represented by the following formula as acomponent: ##STR9## wherein M' is a Group IV-B transition metal;X' andX" are the same or different hydride, halogen, hydrocarbyl orhalohydrocarbyl having up to about 6 carbon atoms; A' and A" are thesame or different asymmetrical mononuclear or polynuclear hydrocarbyl orsilahydrocarbyl moieties; and S' is a bridge of 1-4 atoms selected fromthe group consisting of silanylene, silaalkylene, oxasilanylene andoxasilaalkylene.
 6. A process for polymerizing α-olefins which comprisescontacting alpha-olefins containing two or more carbon atoms underpolymerization conditions with a catalyst system, at least one componentof which is on an inert support, comprising a transition metal compoundrepresented by the following formula as a component: ##STR10## whereinM' is a Group IV-B transition metal;X' and X" are the same or differenthydride, halogen, hydrocarbyl or halohydrocarbyl having up to about 6carbon atoms; A' and A" are the same or different asymmetricalmononuclear or polynuclear hydrocarbyl or silahydrocarbyl moieties; andS' is a bridge of 1-4 atoms selected from the group consisting ofsilanylene, silaalkylene, oxasilanylene and oxasilaalkylene.